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Telecom tech could protect aircraft

Photonics SpectraJan 2011
ANN ARBOR, Mich. – Infrared supercontinuum laser technology could soon help protect
military helicopters from heat-seeking missiles designed to home in on IR radiation
emitted by a helicopter’s engine. Built with off-the-shelf telecom fiber optics,
the laser technology operates in the mid- and longer IR wavelengths. Because it
emits such a broad spectrum of light, it can jam missile sensors from a distance
of 1.8 miles.

Optical parametric oscillators have been used on aircraft to confuse
shoulder-launched heat-seeking missiles, but this technology is expensive and fragile,
not suitable for the rigors of helicopter flight. Current laser-based IR countermeasures,
consisting of 84 pieces of moving optics, are not considered a practical option
for helicopter flight.

Researchers are developing mid-IR supercontinuum laser technology
to protect military helicopters from heat-seeking missiles. Courtesy of Omni Sciences
Inc.
“We moved from complexity to simplicity,” said Mohammed
N. Islam, a professor in the department of electrical engineering and computer science
at the University of Michigan. “The compact system can go anywhere there
is space on the helicopter. We eliminated the need for mode-locked lasers, which
are expensive, and we extended the wavelength to cover the entire spectrum. We used
a standard distributed feedback pump laser, and light can be piped easily through
10- to 15-m fiber. Optical amplifier technology is used to boost the signal.”

Islam and his team created an all-fiber integrated supercontinuum
laser that provides up to 10.5-W time-averaged power with a continuous spectrum
from approximately 0.8 to 4 µm, according to their report in the IEEE Journal of
Selected Topics in Quantum Electronics, March/ April 2009. They stated that the
laser is generated by a combination of standard single-mode fibers and fluoride
fibers pumped by a laser diode-based cladding-pumped fiber amplifier system. They
also demonstrated that the output of the supercontinuum laser pulse pattern can
be adjusted by directly modulating the seed laser diode and controlling the amplifier
gain with a signal feedback technique.

“This is an all-fiber integrated laser with no moving parts.
It is reliable, rugged and easy to maintain. The off-the-shelf components from telephone
networks are relatively inexpensive and are based on a proven technology, Islam
said.”

Reliability, relatively low cost and a basis in proven technology
are attractive qualities to the US Department of Homeland Security, which has been
looking for better ways to protect commercial and military aircraft from shoulder-launched
missile attacks. The laser system is being created at the university and at Islam’s
spin-off company, Omni Sciences Inc. It is being commercialized by the company,
which recently received a total of $1 million in grants from the US Army and DARPA
to build a second-generation prototype, according to a press release from the university.

A second-generation prototype now in development is expected to
have increased power and to be smaller and more rugged. Islam and his team are working
to bring down the weight of the system from 25 to 10 lb or lower. “It is easy
to scale up the power of the laser and to increase repetition rate and pump power
with no real change in architecture,” he said.

Among the challenges for the technology, from the engineering
standpoint, are the thermal management and packaging aspects. The US government
must rate the technology as having advanced from the level at which its components
are validated in a laboratory environment to the level at which its prototype is
demonstrated in a relevant environment.

Scientific hurdles include the need to expand the long wavelength
and increase bandwidth, Islam said. “The supercontinuum laser is a platform
technology and is very flexible for a wide range of applications.” These applications
could include monitoring at national borders, active remote sensing of natural gas
leaks, and, in the medical field, destroying harmful fats and lipids in the human
body in the fight against Type 2 diabetes.

Electromagnetic radiation detectable by the eye, ranging in wavelength from about 400 to 750 nm. In photonic applications light can be considered to cover the nonvisible portion of the spectrum which includes the ultraviolet and the infrared.